Tuftsin Receptor Peptide Construct. Ser. No. 08/660,697 teaches certain locally restricted peptides, in which the biological-function domain and metal-peptide backbone are combined, and the biological-function domain is specific for the tuftsin receptor found on polymorphonuclear (PMN) granulocytes, monocytes and macrophages.
Native tuftsin is a tetrapeptide of the sequence Thr-Lys-Pro-Arg (SEQ ID NO. 1), located as residues 289–292 of the Fc region of the heavy chain of leukokinin (a cytophilic γ-globulin). It is liberated by a combination of two cleavages. The C-terminal peptide bond is cleaved in the spleen by splenic enzyme and subsequent cleavage of the N-terminal peptide bond by enzyme leukokininase which occurs on the membranes of the granulocytes where it acts to stimulate phagocytosis. The tuftsin sequence stimulates macrophages and polymorphonuclear granulocytes towards phagocytosis. This sequence thus has a role in the immune system response for fighting infections and bacteria and other invasions. There are specific tuftsin receptors present on granulocytes and macrophages. The receptor density is approximately 50,000–100,000 per cell, with the receptor-tuftsin complex reported to internalize after binding. Thus a peptide specific for the tuftsin receptor may be used in the treatment of certain diseases, as is disclosed generally in U.S. Pat. No. 4,390,528 to V A Najjar and U.S. Pat. No.5,028,593 to K Nishioka, the teachings of which are incorporated herein by reference.
The '697 application teaches a precursor peptide, incorporating both a metal ion-binding backbone and a tuftsin receptor-specific biological-function domain, which tuftsin receptor-specific domain is biologically active only on labeling or complexing the metal ion-binding backbone with a metal ion, of the following general formula:R1-Aaa-Bbb-Ccc-Ddd-Eee-R2Where:                Aaa=L- or D-configuration residue selected from Thr, Cys, Pen, Pro, or Ser and corresponding des-amino derivatives.        Bbb=L- or D-configuration residue with a positively charged side chain, and containing an N for metal ion complexation, such as Arg, Lys, Orn, homoArg, S-(2-aminoethyl)Cys, O-(2-aminoethyl)Ser and other similar basic amino acids, and derivatives thereof        Ccc=L- or D-configuration residue with an un-charged side chain, and containing an N for metal ion complexation, such as Gly, Ala, Aib, Val, Nle, Leu and similar amino acids with un-charged side chains.        Ddd=L- or D-configuration residue, providing an S, and preferably an S and N, for metal ion complexation, or alternatively two Ns for metal ion complexation, such as Cys, HomoCys, Pen, His and other synthetic or derivatized amino acids.        Eee=L- or D-configuration residue with a positively charged side chain, such as L- or D-isomers of Arg, Lys, Orn, homoArg, S-(2-aminoethyl)Cys, O-(2-aminoethyl)Ser and other similar basic amino acids, and their corresponding des-carboxyl derivatives. A similar aliphatic or aromatic chain with a basic functional group can also be substituted.        R1=H, alkyl, aryl, alkylcarbonyl, arylcarbonyl, alkyloxycarbonyl, aryloxycarbonyl, or a polymer such as PEG, PVA, or polyamino acid, attached directly or through a carbonyl group. R1 does not exist if Aaa is a des-amino amino acid.        R2=amide, substituted amide, ester, or a polymer such as PEG, PVA, or polyamino acid. R2 does not exist if Eee is a des-carboxyl amino acid.        
One representative peptide from this series was the sequence Thr-D-Lys-Gly-D-Cys-Arg (SEQ ID NO. 2). This peptide displayed very high affinity (KD=1–5 nM) for human leukocytes after its binding to reduced TcO[V]. When complexed to radioactive 99mTcO[V], the peptide localizes to the site of inflammation or infection on i.v. administration. The affinity of the peptide which is not complexed to a metal ion is on the order of KD=10−4 M.
The structure of the Thr-D-Lys-Gly-D-Cys-Arg (SEQ ID NO. 2) peptide after binding to technetium is as follows:
The '697 application teaches that this peptide can similarly be labeled with Re, and that similar peptides can also be designed and synthesized using an N4 metal ion-binding domain, such as Thr-D-Lys-Gly-D-His-Arg (SEQ ID NO. 3). Tuftsin receptor-specific peptides disclosed in '697 include Thr-D-Lys-Gly-D-Cys-Arg (SEQ ID NO.4), Thr-D-Lys-Gly-D-His-Arg (SEQ ID NO.3) and Pro-D-Lys-Gly-D-Cys-Arg (SEQ ID NO. 4).
The peptides taught in '697 may be complexed with a non-radioactive ionic form of rhenium or another suitable isotope, thereby creating a non-radioactive metallopeptide drug for the treatment of disease. Such peptides may also be radiolabeled with a diagnostic metal ion, such as 99mTc, and used to determine sites of concentration of granulocytes and macrophages, such as infections and inflammations, or radiolabeled with a therapeutic metal ion, such as 186Re or 188Re, and used in the treatment of disease.
In addition, tuftin has analgesic and other central nervous system effects. See, e.g., Herman et al., “Central Effects of Tuftsin,” in Antineoplastic, Immunogenic and Other Effects of the Tetrapeptide Tuftsin: a Natural Macrophage Activator, Najjar V A and Freidkin M, eds., New York Academy of Sciences, 1983 [hereinafter Antineoplastic], 156–163; Paradowski et al., “The Influence of Tuftsin on Blood Pressure in Animals,” in Antineoplastic, 164–167; Fridkin and Najjar, Crit. Rev. Biochem. Med. Biol., 24 (1989). Herein disclosed are novel peptides and peptidomimetics which are specific for the tuftsin receptor and may be used as an analgesic and in the treatment of various other central nervous system conditions.